The present invention relates to an all-wheel drivetrain for a motor vehicle, which has at least two driven axles, comprising a characteristic torque converter transmission of longitudinal construction, to the input side of which drive power is fed and which serves for converting a characteristic of a drive engine, and the output side of which is connected to a transfer device, by means of which the drive power can be distributed to the two axles, the characteristic torque converter transmission having an output shaft, which is connected to a first drive shaft for the first axle, and a countershaft parallel thereto, the output shaft and the countershaft being connected to one another by means of a first constant transmission ratio, and the countershaft being connected by means of a second constant transmission ratio to a second drive shaft for the second axle.
Such an all-wheel drivetrain is disclosed by DE 102 53 259 A1.
In the document cited an internal combustion engine is connected to an input of a dual clutch arrangement. The output of the dual clutch arrangement is connected to a dual clutch transmission, which comprises an input shaft arrangement, a countershaft and at least one transmission output, which is not aligned coaxially with the one or more transmission input shafts. The dual clutch transmission is embodied as a countershaft transmission.
In one embodiment, the countershaft is connected to the output shaft by a constant output gear train. The output shaft is connected to a first drive shaft for a rear axle. Also supported on the countershaft is a loose gear, which can be connected to the countershaft by means of a transfer device in the form of a selective engagement clutch. The loose gear meshes with a further gear, which is connected to a second drive shaft for the second axle (front axle). The second drive shaft is connected to a front axle transverse differential.
EP 1 321 327 A2 also discloses a longitudinally installed drivetrain for a motor vehicle, in which a transfer box serves to transmit a drive torque on the one hand to a rear axle and on the other hand to a front axle by way of a prop shaft arranged at an angle to the drivetrain longitudinal axis. In this case power is transmitted from the transfer box to the prop shaft via a drive pinion and an output pinion, a universal joint of the prop shaft being arranged at least partially inside the output pinion.
The intention here is to enhance a motor vehicle transmission designed for a rear wheel drive in such a way as to allow a further output to a front axle differential.
The journal Automobiltechnische Zeitschrift (ATZ), issue 2, 2004, Vol. 106, pages 92 to 98, furthermore discloses the flange mounting of a transfer case having a fixed output to the rear axle on the transmission output of a conventional, manual shift transmission. Also coaxially arranged with the output shaft is a selective engagement clutch, which can be connected to a drive shaft for the front axle by way of a hollow shaft and a chain drive.
Such a separate transfer box involves a great weight and takes up a large overall space. A relatively large number of meshing toothed engagements is also required. The weight distribution in the drivetrain is moreover not particularly favourable.